909 research outputs found
Efficient transfer entropy analysis of non-stationary neural time series
Information theory allows us to investigate information processing in neural
systems in terms of information transfer, storage and modification. Especially
the measure of information transfer, transfer entropy, has seen a dramatic
surge of interest in neuroscience. Estimating transfer entropy from two
processes requires the observation of multiple realizations of these processes
to estimate associated probability density functions. To obtain these
observations, available estimators assume stationarity of processes to allow
pooling of observations over time. This assumption however, is a major obstacle
to the application of these estimators in neuroscience as observed processes
are often non-stationary. As a solution, Gomez-Herrero and colleagues
theoretically showed that the stationarity assumption may be avoided by
estimating transfer entropy from an ensemble of realizations. Such an ensemble
is often readily available in neuroscience experiments in the form of
experimental trials. Thus, in this work we combine the ensemble method with a
recently proposed transfer entropy estimator to make transfer entropy
estimation applicable to non-stationary time series. We present an efficient
implementation of the approach that deals with the increased computational
demand of the ensemble method's practical application. In particular, we use a
massively parallel implementation for a graphics processing unit to handle the
computationally most heavy aspects of the ensemble method. We test the
performance and robustness of our implementation on data from simulated
stochastic processes and demonstrate the method's applicability to
magnetoencephalographic data. While we mainly evaluate the proposed method for
neuroscientific data, we expect it to be applicable in a variety of fields that
are concerned with the analysis of information transfer in complex biological,
social, and artificial systems.Comment: 27 pages, 7 figures, submitted to PLOS ON
On the Impact of the Degree of Fluorination on the ORR Limiting Processes within Iron Based Catalysts: A Model Study on Symmetrical Films of Barium Ferrate
In this study, symmetrical films of BaFeO, BaFeOF and BaFeOF were synthesized and the oxygen uptake and conduction was investigated by high temperature impedance spectroscopy under an oxygen atmosphere. The data were analyzed on the basis of an impedance model designed for highly porous mixed ionic electronic conducting (MIEC) electrodes. Variable temperature X-ray diffraction experiments were utilized to estimate the stability window of the oxyfluoride compounds, which yielded a degradation temperature for BaFeOF of 590 °C and a decomposition temperature for BaFeOF of 710 °C. The impedance study revealed a significant change of the catalytic behavior in dependency of the fluorine content. BaFeO revealed a bulk-diffusion limited process, while BaFeOF appeared to exhibit a fast bulk diffusion and a utilization region δ larger than the electrode thickness L (8 μm). In contrast, BaFeOF showed very area specific resistances due to the lack of oxygen vacancies. The activation energy for the uptake and conduction process of oxygen was found to be 0.07/0.29 eV (temperature range-dependent), 0.33 eV and 0.67 eV for BaFeO, BaFeOF and BaFeOF, respectively
Precision and Recall Reject Curves for Classification
For some classification scenarios, it is desirable to use only those
classification instances that a trained model associates with a high certainty.
To obtain such high-certainty instances, previous work has proposed
accuracy-reject curves. Reject curves allow to evaluate and compare the
performance of different certainty measures over a range of thresholds for
accepting or rejecting classifications. However, the accuracy may not be the
most suited evaluation metric for all applications, and instead precision or
recall may be preferable. This is the case, for example, for data with
imbalanced class distributions. We therefore propose reject curves that
evaluate precision and recall, the recall-reject curve and the precision-reject
curve. Using prototype-based classifiers from learning vector quantization, we
first validate the proposed curves on artificial benchmark data against the
accuracy reject curve as a baseline. We then show on imbalanced benchmarks and
medical, real-world data that for these scenarios, the proposed precision- and
recall-curves yield more accurate insights into classifier performance than
accuracy reject curves.Comment: 11 pages, 3 figures. Updated figure label
Sentinel-1 Imaging Performance Verification with TerraSAR-X
This paper presents dedicated analyses of TerraSAR-X data with respect to the Sentinel-1 TOPS imaging mode.
First, the analysis of Doppler centroid behaviour for high azimuth steering angles, as occurs in TOPS imaging, is
investigated followed by the analysis and compensation of residual scalloping. Finally, the Flexible-Dynamic
BAQ (FD-BAQ) raw data compression algorithm is investigated for the first time with real TerraSAR-X data
and its performance is compared to state-of-the-art BAQ algorithms. The presented analyses demonstrate the
improvements of the new TOPS imaging mode as well as the new FD-BAQ data compression algorithm for
SAR image quality in general and in particular for Sentinel-1
Understanding Concept Identification as Consistent Data Clustering Across Multiple Feature Spaces
Identifying meaningful concepts in large data sets can provide valuable
insights into engineering design problems. Concept identification aims at
identifying non-overlapping groups of design instances that are similar in a
joint space of all features, but which are also similar when considering only
subsets of features. These subsets usually comprise features that characterize
a design with respect to one specific context, for example, constructive design
parameters, performance values, or operation modes. It is desirable to evaluate
the quality of design concepts by considering several of these feature subsets
in isolation. In particular, meaningful concepts should not only identify
dense, well separated groups of data instances, but also provide
non-overlapping groups of data that persist when considering pre-defined
feature subsets separately. In this work, we propose to view concept
identification as a special form of clustering algorithm with a broad range of
potential applications beyond engineering design. To illustrate the differences
between concept identification and classical clustering algorithms, we apply a
recently proposed concept identification algorithm to two synthetic data sets
and show the differences in identified solutions. In addition, we introduce the
mutual information measure as a metric to evaluate whether solutions return
consistent clusters across relevant subsets. To support the novel understanding
of concept identification, we consider a simulated data set from a
decision-making problem in the energy management domain and show that the
identified clusters are more interpretable with respect to relevant feature
subsets than clusters found by common clustering algorithms and are thus more
suitable to support a decision maker.Comment: 10 pages, 6 figures, to be published in proceedings of 2022 IEEE
International Conference on Data Mining Workshops (ICDMW
In-Orbit SAR Performance of TerraSAR-X
TerraSAR-X is the first German Radar satellite for scientific and commercial applications. The project is a public-private partnership between DLR and EADS Astrium GmbH. TerraSAR-X consists of a high resolution Synthetic Aperture Radar at X-Band. The radar antenna is based on active phased array technology that allows the control of many different instrument parameters and operational modes (Stripmap, ScanSAR and Spotlight) with various polarizations.
Following the TerraSAR-X launch, scheduled for February 2007, it is planned a six month Commissioning Phase covering the characterization and verification of the SAR mission. Within this phase, the Overall SAR System Performance (OSSP) takes care of the correct working and interaction of all SAR system elements essential for obtaining an optimum SAR Performance.
The paper covers the first in-orbit characterization and verification results of the SAR system performance for TerraSAR-X operational and experimental modes. This characterization is divided into four phases: Initial Characterization, Scene Characterization –both mostly based on basic and experimental products-, and Verification of TS-X Instrument Command Generation.
The different optimization strategies and performance trade-offs are discussed and presented in the paper, including very first TerraSAR-X images. The result of the real SAR data analysis determines the final system baseline and thus the final image quality, e.g. Temperature compensation, Total Zero Doppler Steering, Up/down chirp toggling, transmitted bandwidth, timing interferences, etc.
The first section of the paper introduces the activities carried out during the Commissioning Phase for the TerraSAR-X SAR system performance characterization/verification. In the second section, the strategies for the performance optimization and characterization are presented. Finally, the in-orbit SAR performance results are given in section three
Quantifying the predictability of visual scanpaths using active information storage
Entropy-based measures are an important tool for studying human gaze behavior
under various conditions. In particular, gaze transition entropy (GTE) is a
popular method to quantify the predictability of fixation transitions. However,
GTE does not account for temporal dependencies beyond two consecutive fixations
and may thus underestimate a scanpath's actual predictability. Instead, we
propose to quantify scanpath predictability by estimating the active
information storage (AIS), which can account for dependencies spanning multiple
fixations. AIS is calculated as the mutual information between a processes'
multivariate past state and its next value. It is thus able to measure how much
information a sequence of past fixations provides about the next fixation,
hence covering a longer temporal horizon. Applying the proposed approach, we
were able to distinguish between induced observer states based on estimated
AIS, providing first evidence that AIS may be used in the inference of user
states to improve human-machine interaction.Comment: 19 pages, 3 figure
Scalloping Correction in TOPS Imaging Mode SAR Data
This paper presents an investigation on scalloping correction in the TOPS imaging mode for SAR systems with electronically steered phased array antennas. A theoretical simulation of the scalloping is performed and two correction methods are introduced. The simulation is based on a general cardinal sine (sinc) antenna model as well as on the TerraSAR-X antenna model. Real TerraSAR-X data acquired over rainforest are used for demonstration and verification of the scalloping simulation and correction. Furthermore a calibration approach taking into account the special TOPS imaging mode properties is introduced
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